This application is related to and claims priority from Japanese Patent Applications No. Hei. 11-68871 filed on Mar. 15, 1999 and No. Hei. 11-354817 filed on Dec. 14, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a vapor-compression type refrigerant cycle system in which expansion energy in an expansion unit is recovered. The present invention is suitably applied to a refrigerant cycle system in which refrigerant such as ethylene, ethane, nitrogen oxide, or carbon dioxide is used so that pressure of refrigerant discharged from a compressor exceeds critical pressure.
2. Description of Related Art
In a conventional vapor-compression type refrigerant cycle, after compressed refrigerant is cooled and is press-reduced, low-pressure refrigerant is evaporated in an evaporator so that refrigerating effect is obtained. However, in the conventional refrigerant cycle, the refrigerating effect is determined based on an enthalpy difference of refrigerant between an inlet side and an outlet side of the evaporator. Therefore, when temperature within the evaporator increases and pressure within the evaporator (i.e., pressure at a refrigerant inlet of the evaporator) increases, the enthalpy difference of refrigerant between the inlet side and the outlet side of the evaporator becomes smaller, and the refrigerating effect of the refrigerant cycle decreases.
In view of the foregoing problems, it is an object of the present invention to provide a refrigerant cycle system which prevents refrigerating effect from being greatly decreased even when pressure within an evaporator is increased.
According to an aspect of the present invention, a refrigerant cycle system includes a radiator for cooling a compressed refrigerant, an inner heat exchanger in which refrigerant from the radiator branches into first-flow refrigerant and second-flow refrigerant and the second-flow refrigerant is decompressed to perform a heat exchange between the first-flow refrigerant and the decompressed second-flow refrigerant, an expansion unit for decompressing and expanding the first-flow refrigerant having been heat-exchanged with the second-flow refrigerant, an expansion-energy recovering unit for converting expansion energy during a refrigerant expansion in the expansion unit to mechanical energy, and an evaporator for evaporating refrigerant from the expansion unit. The expansion-energy recovering unit is disposed to compress refrigerant flowing into the radiator using the mechanical energy. Thus, an enthalpy difference between a refrigerant inlet side and a refrigerant outlet side of the evaporator is increased by the conversion energy from the expansion energy to the mechanical energy. Therefore, even when the pressure within the evaporator increases, refrigerating effect is prevented from being greatly reduced. Further, because refrigerant flowing into the radiator is compressed using the converted mechanical energy, a compression operation amount is reduced in the while refrigerant cycle system, and coefficient of performance is improved relative to the compression operation amount.
According to an another aspect of the present invention, an expansion unit for decompressing and expanding refrigerant discharged from the radiator is disposed to recover expansion energy during a refrigerant expansion, and a control unit controls a relation amount relative to operation of the expansion unit to control a pressure of high-pressure side refrigerant having been compressed by the compressor and before being decompressed by the expansion unit. Because the refrigerant cycle system operates while the expansion energy is recovered, actual consumption power in the refrigerant cycle system is reduced, and coefficient of performance of the refrigerant cycle system is improved. Therefore, even when the compression operation amount of a compressor increases for preventing the refrigerating effect from reducing when temperature within the evaporator increases, actual consumption power of the compressor is prevented from increasing. Accordingly, even when the pressure within the evaporator increases, the refrigerant cycle system prevents the refrigerating effect from being greatly decreased.
For example, the relation amount relative to the operation of the expansion unit is an energy amount recovered during a refrigerant expansion of the expansion unit, is a refrigerant amount flowing through the expansion unit, or a driving force which is necessary for driving the expansion unit.
Preferably, the control unit controls the pressure of the high-pressure side refrigerant to become a target pressure determined based on a refrigerant temperature at a refrigerant outlet of the radiator. Therefore, the refrigerating effect is further improved in the refrigerant cycle system.